1. Field of the Invention
The present invention relates to a content delivery system composed of a communication terminal apparatus having means for reception via a plurality of communication paths and of a communication apparatus for providing a content delivery service to the communication terminal apparatus and to a terminal apparatus.
2. Description of Related Art
With the diversification of life styles and working patterns, demand has grown for a communication service which is available at any time and anywhere through connection to the Internet using a mobile terminal such as a mobile phone, a PDA, or a note-type personal computer. Owing to the recent advances in mobile communication technology, a plurality of mobile communication networks including Wireless LAN, W-CDMA, cdma 2000, and Bluetooth are usable at present. A mobile terminal is capable of connection to each of the communication networks by using a communication adaptor supported by the corresponding one of the communication networks. The mounting of a plurality of communication adaptors on one mobile terminal has made it possible to select an optimum communication network depending on the speed of received data or a communication situation at the mobile terminal and dynamically switch the communication network.
In the case of dynamically switching the communication path, while the mobile terminal is receiving a content delivery service through connection to the server, and continuing the content delivery service, it is typical for a proxy apparatus or an agent present on a communication path to constantly preserve session information for the content delivery service and continue the delivery service by using the session information in the content delivery service on a communication path after switching.
The session used herein indicates a communication flow between a transmitting apparatus providing a given communication service and a receiving apparatus and a set of sequential processes executed at each of the transmitting and receiving apparatus to provide the communication service. The session information is general information on a session for providing the service. As examples of the session information, there can be listed, e.g., the IP addresses and port numbers of server/client terminals, a communication protocol, a session start time, a time elapsed from the beginning of the service, a service name, and the name of an application in use.
For the continuation of a delivery service on the switching of a communication path, there has been proposed a method in which session managing means switches the condition of a session in response to a request from a mobile terminal, while delivered data is received by a user., and thereby switches the terminal (see, e.g., Patent Document 1) and a method which exchanges session information for a delivery service between proxys in response to a request from a session managing unit and thereby flexibly performs the switching of a communication path at a mobile terminal (see, e.g., Patent Document 2).    [Patent Document 1] JP-A No. 176432/2002    [Patent Document 2] JP-A No. 64562/2002
However, each of the foregoing conventional methods for switching a delivery service upon the switching of a communication path temporarily intermits a session at a mobile terminal, switches the communication path, and then resumes the session. As a result, a problem has occurred in a delivery service in which the continuity of received data greatly affects the quality of the service that a temporarily interrupted session as described above causes user discomfort. Another problem is that, if the characteristic of a communication path, such as a communication speed, prior to switching is different from that of a communication path after switching, it is difficult to continue the same service.
Specifically, the foregoing technology disclosed in Patent Document 1 cannot provide the delivery service without temporary interruption at the same terminal. The technology disclosed in Patent Document 2 also encounters the interruption of the delivery service during the period of switching from one communication path to the other at the mobile terminal.